Numbers

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Numbers are tricky. When you write them out and when you use numerals depends on what kind of writing you are doing.

Academic Writing

In strictly academic writing, spell out numbers of one or two words.
  • Anthony was able to bike five miles in less than an hour. (Notice that 5 is written out because it's one word.)
  • Maria bought five bananas, two bunches of grapes, and six oranges for her fruit salad. She needed twenty-one servings for the luncheon. (Notice that each number is written out including 21.)

Numbers that are more than two words should be written as numerals.
  • Our vacation to North Caroline ended up being 728 miles round trip. (Can you imagine writing out seven hundred twenty-eight miles?)
  • Tony was born in the fall of 1966. (Writing years are numerals is just more practical).
In addition, the following numbers are written as numerals:
  • Dates - December 7, 1941, 32 BC, AD 1066
  • Addresses - 119 Lakewood Lane, 1600 Pennsylvania Avenue
  • Percentages - 45 percent or 45%
  • Fractions and Decimals - 1/3 and 0.25
  • Scores - 20 to 13 or 15-18
  • Statistics - average age 25
  • Surveys - 2 out of 5
  • Exact amounts of money - $861.34 or $0.67
  • Divisions of books - volume 6 or chapter 5
  • Divisions of plays - act 2, scene 4
  • Time of day - 12:00 a.m. or 4:35 p.m.
Often, the handbook assigned to you for writing classes is a great guide. Refer to it.

Technical Writing

Numbers in technical writing vary considerably. Often you have to consult the style guid that your organiztion or instructor uses. If you are taking a course, look at your textbook for how it handles numbers and ask your instructor which rules to follow.
Some handbooks will say write out numbers lower than 10 or lower than 20. Others will have a more complex set of rules to follow. Mike Markel's Technical Communication 9th Edition gives these rules:
  1. Technical quantities of any amount are expressed in numerals, especially if a unit of measurement is included:
    1. 3 feet
    2. 12 grams
    3. 43,219 square miles
    4. 36 hectares
  2. Nontechnical quantities of fewer than 10 are expressed in words:
    1. three people
    2. six whales
  3. Nontechnical quantities of 10 or more are expressed in numerals:
    1. 300 people
    2. 12 whales
  4. Approximations are written out:
    1. approximately ten thousand people
    2. about two million trees
  5. Round numbers over nine million are expressed in both words and numerals
    1. 14 million light years
    2. $64 billion
  6. Decimals are expressed in numerals:
    1. 3.14
    2. 1,013.065
    3. Decimals of less than one should be preceeded by a zero:
      1. 0.146
      2. 0.006
  7. Fractions are written out, unless they are linked to technical units:
    1. two-thirds of the members
    2. 3 1/2 hp
  8. Time of day is expressed in numerals if A.M. or P.M. is used; otherwise, it is written out:
    1. 6:10 A.M.
    2. six o'clock
    3. the nine-thirty train
  9. Page number and titles of figures and tables are expressed in numerals:
    1. Figure 1
    2. Table 13
    3. page 261
  10. Back-to-back numbers are written using both words and numerals:
    1. six 3-inch screws
    2. fourteen 12-foot ladders
    3. 3,012 five-peice starter units
  11. Numbers in legal contracts or in documents intended for international readers should be represented in both words and numerals:
    1. thirty-seven thousand dollars ($37,000)
    2. five (5) relays
  12. Street addresses may require both words and numerals:
    1. 3801 Fifteenth Street


Special Cases

These special cases are also according to Markel's book:
  • A number at the beginning of a sentence should be spelled out:
    • Thirty-seven acres was the size of the lot.
    • The lot was 37 acres. (Many writers would revise the sentence to avoid this problem.)
  • Within a sentence, the same unit of measurement should be expressed consistently in either numerals or words:
    • INCORRECT - On Tuesday the attendance was 13; on Wednesday, eight.
    • CORRECT - On Tuesday the attendance was 13; on Wednesday, 8.
    • CORRECT - On Tuesday the attendance was thirteen; on Wednesday, eight.
  • In general, months should not be expressed as numbers. In the United States, 3/7/09 means March 7, 2009; in many other countries, it means July 3, 2009. The following forms, in which the months are written out, are preferable:
    • March 7, 2009
    • 7 March 2009